1. Field of the Invention
The present invention relates to an optical glass and a manufacturing method, thereof, and in particular to a manufacturing method of the optical glass that prevents deterioration of the burner used for synthesizing the glass particles that form the optical glass, and obtains an optical glass having a stable quality.
2. Description of the Related Art
As a manufacturing method of an optical fiber perform as an example of an optical glass, there are methods such as the VAD method, OVD method, MCVD method, PCVD method and the like. Among these, in the OVD (Outside Vapor Phase Deposition) method, a glass source material gas such as silicon tetrachloride (SiCl4) is ejected along with a doping gas such as oxygen or hydrogen, an inflammable gas such as hydrogen, and a combustion-supporting gas such as oxygen, and the glass particles are synthesized by hydrolyzed or oxidized the glass source material gas in the flame. Glass particles (soot) are deposited in the radial direction on the peripheral portion of the cylindrical starting material that rotates around its axis and provides the glass that will become a core, and a porous layer comprising a plurality of layers is formed so as to provide a porous body for the optical fiber. This porous body is converted into a transparent glass in an electrical furnace, and thereby the optical fiber perform is manufactured (refer to U.S. Pat. No. 5,597,398).
The optical glass manufactured by this method can be satisfactorily used for an optical glass for semiconductor manufacturing apparatuses, not just for optical fibers.
As the burners for glass syntheses used in the manufacture of the porous body for the optical fiber, multiple pipe burners wherein a plurality of discharge openings for each type of gas used in the synthesis of glass particles are provided in a concentric form or a multi-nozzle type burner wherein a plurality of discharge openings for a combustion-supporting gas are provided concentrically between a plurality of discharge openings for inflammable gasses, are known (refer to U.S. Pat. No. 4,810,189). These burners are generally made of a silica glass.
However, accompanying the increase in telecommunication demand in recent years, the demand for optical fiber has been increasing year by year. Thus, lowering the price of the optical fiber is desirable. In order to respond to this demand, the manufacturing speed of the optical fiber must be accelerated, the manufacture of optical fiber must be made more efficient, the optical fibers must be manufactured in large amounts, and the manufacturing cost must be reduced. Therefore, in order to manufacture a large amount of optical fiber at one time and thereby reduce the manufacturing cost, there is a trend to enlarge the size of the optical fiber preform used to form the optical fiber.
In addition, accompanying the increasing size of the semiconductor manufacturing apparatuses, the size of the optical glass for the semiconductor manufacturing apparatus is also enlarged.
When the size of the optical glass for the preform or the optical glass used for semiconductor manufacturing apparatuses is enlarged, for example, in the manufacture of optical glass by the OVD method or the like, improving the speed of depositing the glass particles on the outer circumference of the starting material (hereinafter referred to as “the deposition speed”) and the efficiency of depositing the glass particles on the outer circumference of the starter material (hereinafter, referred to as “the deposition efficiency”) is an extremely important problem.
The deposition speed of the glass particles can be improved by improving the synthesis speed of the glass particles. Thus, in order to improve the synthesis speed of the glass particles, it is necessary to lengthen the reaction time of the glass source material gas and to increase and the reaction temperature.
In addition, in order to increase the deposition efficiency of the glass particles, the temperature difference between the deposition surface for the glass particles and the flame that is ejected from the burner for glass synthesis must be made large, and the thermolytic effect (the effect wherein the glass particles receive a force that is proportional to the temperature gradient from each type of gas that is used in the synthesis of the glass particles) must be maximally used.
However, when the temperature of the flame is made high, the end face of the burner for glass synthesis is heated and may be fused and lost. When the burner for glass synthesis is lost, this burner for glass synthesis becomes unusable for the manufacture of the optical glass, and thus replacement of the burner for glass synthesis must be carried out frequently. Therefore, it is not possible to improve the deposition speed or deposition efficiency of the glass particles, and not possible to reduce the manufacturing cost.
In addition, when the end face of the burner for glass synthesis is deformed by loss due to heating, it is not possible to form a stable flame, and the deposition speed and the deposition efficiency of the glass particles decrease. Furthermore, there are the problems that glass fragments that are produced by the end face of the burner for glass synthesis being lost are deposited along with the glass particles, these glass fragments cause the production of bubbles and/or other defects (scratches and foreign particles) in the optical glass.
The present invention is provided in consideration of the problems described above, and an object of the present invention to provide a manufacturing method of optical glass that prevents deterioration of the burner used in synthesizing the glass particles that form the optical glass, and obtains an optical glass having a stable quality.